1. Field of the Invention
This invention relates to a modified absorption system and process that operates around a crystallization curve of a solution with a crystallization limitation.
2. Description of Prior Art
Conventional absorption refrigeration cycles are well known to those persons skilled in the art of heating, air conditioning and refrigeration. A known system based upon such conventional absorption cycles uses a solution that contains a refrigerant and an absorbent. The refrigerant typically flows from a generator to a condensor, an evaporator, an absorber, a solution pump, and then back to the generator. The absorbent typically flows from the generator to the absorber and then back to the generator, by way of the solution pump.
A conventional cycle for a water-absorption refrigeration machine, that operates with water-lithium bromide as the solution, also includes a liquid heat exchanger for transferring heat between the absorbent and the refrigerant-absorbent streams. However, when using water-lithium bromide as the solution, conventional cycles must be operated so that crystallization of the salt does not occur, particularly during shutdown of the system. Thus, in actual practice of such conventional cycles, relatively low concentrations of lithium bromide solutions are commonly used in small commercial units to insure against crystallization of the salt. Typical relatively low concentrations of 54% and 58.5% are used in such conventional cycles. Higher concentrations, such as about 60% and 64.5% are used in larger commercial units so that the absorber can be operated at a higher temperature. In order to avoid crystallization of the salt, controls and a shutdown dilution cycle are commonly used with such larger commercial units.
U.S. Pat. No. 5,016,448 discloses an internal heat exchanger for an absorption apparatus. A strong solution is drawn into an eductor which also receives a supply of weak solution from a pump. The strong solution is mixed with the weak solution at the eductor to form an intermediate solution having a concentration between the concentrations of the strong solution and the weak solution. The intermediate solution is discharged from the eductor and supplied to a manifold which includes several spray nozzles that distribute the intermediate solution over coils within the absorber.
U.S. Pat. No. 5,044,174 teaches an absorption type refrigerating machine wherein the solution is pumped from a first absorber stage directly to a spray nozzle within a second absorber stage. The first absorber stage is combined with a first evaporator stage and the second absorber stage is combined with a second evaporator stage to respectively form separate units.
U.S. Pat. No. 5,016,445 teaches an absorption apparatus wherein one pump transfers fluid from an absorber reservoir at the bottom of an inner cylindrical house to a generator reservoir at the bottom of an outer spherical house. Another pump transfers fluid from the generator reservoir to absorber spray heads which are positioned within the inner cylindrical house. An evaporator is positioned beneath the condensor in the housing for receiving refrigerant liquid from the condensor and for vaporizing the refrigerant to create a refrigerant effect.
U.S. Pat. No. 4,484,456 discloses a triple loop heat exchanger for an absorption refrigeration system which includes a bypass for conducting strong solution from a generator directly to an absorber of the refrigeration system, when strong solution builds to an undesirable level in the generator. Solution within the absorber passes through two heat exchangers in series and then into a generator.
U.S. Pat. No. 4,921,515 teaches a regenerative absorption refrigeration cycle having a plurality of subcycles. The lowest subcycle is a single-effect regenerative absorption cycle. One of the subcycles is a single-effect absorption topping cycle which includes an absorber. A pump is connected between an absorber outlet and a boiler inlet to pump fluid from the absorber back into the boiler.
U.S. Pat. No. 4,246,762 discloses an absorption refrigeration system having a generator section and an absorber section wherein all of the solution from the absorber section is pumped through a heat exchanger and into the generator section. U.S. Pat. No. 4,458,500 teaches an absorption heat pump cycle wherein absorbent solution which is diluted in an absorber accumulates in the bottom of the vessel and the diluted absorbent liquid flows through conduits to a desorber. The diluted absorbent is discharged from the desorber in the form of fine droplets.
U.S. Pat. No. 3,597,936 teaches a process and apparatus for continuously purging gases from an absorber and a condensor. Liquid from within an evaporator section is recirculated and sprayed over an exchange coil within the evaporator section. U.S. Pat. No. 4,877,080 teaches a process and apparatus for cooling a fluid by using lower water vapor pressure above a fluid, such as water-salt solutions of lithium bromide. Cooled absorption liquid is fed to an absorber wherein the cooled absorption liquid absorbs moisture from a stream of air.
U.S. Pat. No. 4,337,625 discloses a waste heat driven absorption refrigeration process and system wherein an intermediate absorber and a low absorber are used along with an intermediate desorber and a high desorber. U.S. Pat. No. 3,742,728 teaches a multi-stage absorption refrigeration system which uses different concentrations of lithium bromide solutions.
In view of the discussed teachings of the prior art references and the conventional absorption cycles and systems, it is apparent that there exists a need for an absorption cycle that operates around a crystallization curve of a solution with a crystallization limitation. A system and process that operates according to such modified absorption cycle could simplify the absorber design and thus reduce the material and construction costs of the absorber. Also, such modified absorption cycle could operate with higher concentrations and higher concentration bandwidths, relative to conventional absorption systems, without intersecting the crystallization curve of the solution. By operating with such higher concentrations, particularly by operating around the crystallization curve, the system would require smaller solution heat exchangers and it would be easier to employ air-cooled heat exchangers, as compared to other conventional absorption systems.